A smoking pipe attachable to one end of a cigarette as a rod-shaped smoking article is disclosed, for example, in Unexamined Japanese Utility Model Publication No. 51-65988 (Document 1). The smoking pipe of Document 1 includes a socket portion formed in one end of the pipe and is capable of receiving one end of a cigarette, a mouthpiece formed in the other end, and a filter contained in the filter holder. The filter is positioned in between the socket portion and the mouthpiece.
Before the cigarette is smoked, the smoking pipe is attached to one end of a cigarette. A smoker then lights the other end of the cigarette and puts the mouthpiece of the smoking pipe in his/her mouth. By so doing, the smoker can smoke the cigarette. At this point, the mainstream smoke of the cigarette passes through the filter in the smoking pipe and is sent from the mouthpiece into the smoker's mouth. Therefore, a part of particle-phase components, such as tar and nicotine in the mainstream smoke is trapped by the filter. Therefore, the smoker can enjoy a mild smoking feeling.
However, the filter of the smoking pipe of Document 1 is not capable of reducing vapor-phase components (acetaldehyde, acetone, benzene, etc.) and gas-phase components (CO, NO, etc.) which are contained in the mainstream smoke. As a result, the vapor-phase components and the gas-phase components are not removed with the filter and sent into the smoker's mouth.
In this respect, a filter cigarette disclosed in Unexamined Japanese Patent Publication No. 11-346748 (Document 2) has a perforation line formed in a tip paper of the cigarette. A smoking pipe disclosed in Unexamined Japanese Patent Publication No. 56-15683 (Document 3) includes a perforation line formed in an outer circumferential wall of the pipe. During smoking, the perforation line allows the outside air to flow into the filter, and the introduced air dilutes mainstream smoke. This dilution of the mainstream smoke reduces not only the particle-phase components such as tar and nicotine, which are actually sent into the smoker's mouth, but also the vapor-phase and gas-phase components.
In the case of the dilution-type filter cigarette and smoking pipe, when a dilution rate of the mainstream smoke is excessively high, a tar amount in the mainstream smoke which is sent into the smoker's mouth, that is, a nicotine amount in the tar, is undesirably reduced. As a result, the smoker cannot enjoy the original flavor and taste of the cigarette. In this point, Document 2 discloses that a reduction rate of the tar (T) is suppressed, as compared to a reduction rate of CO, by locating the perforation line upstream from the filter as viewed in the flowing direction of the mainstream smoke. It can be considered that, according to the filter cigarette of Document 2, a value of C/T (=CO/T) is reduced, so that a desired tar amount to be sent into the smoker's mouth can be secured. In this respect, in the case of the smoking pipe of Document 3, too, the perforations are positioned upstream from the filter. Therefore, the smoking pipe of Document 3 may have the same advantages as the filter cigarette of Document 2.
In the case of the filter cigarette of Document 2, in order to position the perforation line upstream from the filter, the perforation line has to be located in the end portion of the tip paper on the cigarette side. The end portion of the tip paper, however, is an important element for joining the filter and the cigarette together, so that the end portion of the tip paper needs to be firmly bonded to the cigarette. That is to say, it is required that glue be applied to the entire inner surface of the end portion of the tip paper. When the perforation line is located in the end portion of the tip paper regardless of this requirement, glue is applied onto the inner surface of the end portion except for the perforation line, and it is impossible to secure an adequate glue-applied area. As a result, bond strength between the filter and the cigarette is low, and it is then practically difficult to form the perforation line in the end portion of the tip paper.
In this respect, according to Document 3, the perforation line is formed in the smoking pipe itself. Therefore, the smoking pipe of the Document 3 does not have the above problem seen in the filter cigarette of Document 2. However, according to Documents 2 and 3, there is the possibility that the perforation line would be partially blocked by smoker's fingers during smoking. When the perforation line is blocked even partially, air intake into the filter becomes insufficient, and mainstream smoke is not diluted as desired.
It is preferable that the above-mentioned smoking pipe be capable not only of performing a conventional basic treatment for removing tar from the mainstream smoke and diluting the vapor-phase and gas-phase components but also of carrying out an adding treatment for adding flavor such as menthol to the mainstream smoke during smoking.